Investigation of the Influence of Leakages on Non Axisymmetric Endwall Contouring Applied on 3D Steam Turbine Airfoils

Abstract

Tangential endwall contouring is intended to improve the blading efficiency in turbomachinery. The present paper focusses on the influence of leakage flows on the performance of non-axisymmetric endwall contouring. All tests were conducted on a 2 stage axial turbine test rig at the Institute of Power Plant Technology, Steam and Gas Turbines (IKDG) of RWTH Aachen University. The test rig is driven with air. Two sealing setups are applied to create two different leakage mass flows. Four operating points are investigated that represent the design point as well as over load and part load conditions. The endwall contouring is applied on both hub and casing sides. Three configurations are compared. A baseline design without endwall contouring, contoured stator vanes and non-contoured rotor blades as well as contoured vanes and blades. At first, all configurations are investigated with a negligible leakage flow rate at the casing side. The results show that the vane contoured configuration performs best in stage 1 while the fully contoured set-up loses in efficiency for the design point and in part load compared to baseline. This trend is flipped in stage 2 as the full contoured version performs best and the vane contoured configuration loses significantly. This finding is suggesting that endwall contouring has the potential to increase the efficiency. The second focus is put on the interaction of endwall contouring and leakage flow. These investigations show that neither the vane contoured nor the fully contoured set up show an increased efficiency at any operating point. The trends within the first stage are similar to the measurements with the low amount of leakage flow. In the second stage both contouring designs perform worse than the baseline leading to the assumption that the change in efficiency is mainly caused by the re-entering leakage mass flow upstream the contouring and not by the flow that is sucked into the cavities in front of the rotor contouring.